In certain of the hitherto known electropolymerization deposition processes for forming a film of a composite material onto an electrically conductive surface, the dopant is formed by an inert load which is mechanically suspended an the electrolysis bath. This dopant is thus enclosed in the developing matrix and is codeposited without having reacted electrochemically onto said electrically conductive surface. In this way it is possible to incorporate for example titanium oxide in polypyrrole films onto an electrically conductive surface.
In the broad field of conductive polymers, the term dopant is used frequently but does not necessarily imply that it is incorporated as a result of a redox phenomenon but it does refer to a counter-ion of the conductive polymer which is indispensable for the electroneutrality of the deposit in its conductive form.
In other known processes, the dopant is formed by an active substance, more particularly as to redox reactions, and is fixed in advance onto the monomer. In this way, the formed film comprises a chemically bound entity which modifies the properties thereof.
An example wherein this latter process is applied is the modification of monomers which are precursors of conductive polymers, such as pyrrole, thiophene, by reaction with diverse groups such as ferrocene, etheroxides, alkyls, having an activity in very different fields such as oxidoreduction, complexation, and conductivity.
These known processes involve different drawbacks.
Indeed, when use is made as dopant of an inert substance suspended in the electrolysis bath, problems may arise, especially for relatively thin films, as to the homogeneity of the film deposited onto the electrically conductive surface.
If use is made of a process wherein the dopant is formed by an active substance, the monomer has to be modified chemically. This is an operation which cannot be performed onto all of the monomers, which considerably limits application of this process.